The problem whether the northern Tarim craton was an active continental margin during the Paleozoic is of great significance for us to understand the subduction style of paleo-oceanic plates in the Tianshan orogenic belt and the accretion history of the southwestern Central Asian orogenic belt. In northern Tarim, there exists a discontinuously exposed intrusive rock belt, which extends from Hulashan through Heiyingshan - Miledong -Korla to Quruqtagh. In this paper, four granitoid plutons, i.e., Oxidaban pluton, Tiemenguan plution, southeast Tiemenguan plution and Bosten Lake Township pluton, were chosen for geochronological, petrological and geochemical investigations. Zircon LA-ICP-MS U-Pb dating of two samples from southeast Tiemenguan plution and Bosten Lake Township pluton yielded age of 419.2Ma±3.1Ma and 418Ma±2.7Ma respectively. Geochemical data suggest that these granitiods are calcium alkaline - high potassium calcium alkaline Ⅰ type granite characterized by enrichment of Rb, K, U and relative depletion of Nb, Ta, Ti, P, thus geochemically resembling the plate convergence edge volcanic arc granite. Based on the regional magmatism and previous studies, the authors inferred that the South Tianshan Ocean experienced double-direction subduction during early Paleo- zoic period and started southward subduction-reduction in Silurian period which continued to the early Carboniferous, and its closure took place in the late Carboniferous period.%塔里木北缘在古生代是否是主动大陆边缘对于了解南天山洋的俯冲方式及中亚造山带西南缘的增生历史具有重要意义.塔里木北缘断续出露一条侵入岩带,西起老虎台,经黑英山—密勒洞—野云沟-库尔勒一带,再往东与库鲁克塔格地块的侵入岩连在一起.选取志留纪欧西达坂岩体、铁门关岩体、铁门关东南岩体和博斯腾湖乡岩体作为典型岩体进行定年、岩石学和地球化学的研究.获得铁门关东南岩体的锆石U-Pb年龄为419.2Ma±3.1Ma,博斯腾乡岩体的锆石U-Pb年龄为418Ma±2.7Ma.地球化学特征显示,志留纪侵入岩为钙碱性—高钾钙碱性Ⅰ型花岗岩,微量元素富集Rb、K、U等大离子亲石元素(LILE)、亏损Nb、Ta、Ti、P等高场强元素(HFSE),具有板块汇聚边缘火山弧花岗岩的地球化学特征.综合区域地质资料及前人成果,推测在早古生代南天山洋存在双向俯冲,并从志留纪已经开始向南俯冲-消减,一直延续到早石炭世,到晚石炭世闭合.
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